The amount of information has been increasing with the development of information society. In order to cope with the increase in the amount of information, an information recording method having a drastically high recording density, and a recording and reproducing device based on such recording method are expected.
As a recording method that realizes the high density recording, attention is directed to an optical recording method in which a minute opening smaller than a wavelength of incident light is produced, and the light emitted from the opening is utilized to form a beam spot smaller than the wave length of the light.
As conventional minute opening of the optical recording method, an opening which is provided at the sharpened tip of an optical fiber is known, as described in the Patent Document 1. That is, the optical fiber with the sharpened tip is covered with a metal film, and a part of the covered and sharpened portion is cut by a particle beam such as a focusing ion beam (FIB), for producing an opening.
As another prior art, a method that produces an opening having an inclined face on a planar plate is disclosed in the Patent Document 2. That is, a Si substrate is patterned by photolithography, and the resultant pattern is anisotropic etched to produce a reverse pyramid type recess, and the tip of the reverse pyramid, which is the deepest part of the substrate, is made to penetrate to the back side of the substrate. As the penetration method, a method of polishing the rear surface of the Si substrate and an etching method are known.
A vapor deposition method that deposits a metal on the tip of the sharpened core of an optical fiber that improves the light propagation efficiency is also disclosed in the Non-Patent Document 1.
Alternatively, a shape of an optical fiber that improves both the beam spot size and the propagation efficiency is disclosed in the Non-Patent Document 2.
In an example of the light irradiation head disclosed in the Patent Document 3, there is also disclosed a construction wherein the light irradiation head has a head shape of planer structure produced with a symmetrical two dimensional pattern in which a high refractive index dielectric material in the head is formed to be a trapezoidal shape, so that the spot diameter is reduced by the trapezoidal slope and the planer structure.
(Patent Document 1)
Japanese Patent Laid-Open No. 10-206660
(Patent Document 2)
U.S. Pat. No. 5,689,480
(Patent Document 3)
Japanese Patent Laid-Open No. 2002-188579
(Non-Patent Document 1)
“Optical Review”, 1998, Vol 5, No. 6, p 369–373
(Non-Patent Document 2)
“Applied Physics Letters”, Vol 73, No. 15
The conventional methods that form a minute opening by sharpening the tip of an optical fiber have problems relating to an unevenly deposited metallic film and to an unstable etching rate caused by the concentration of the etching solution and by the material composition of the optical fiber.
Also, there are problems in the mass production process, such as the instability in producing an optical fiber with a conically sharpened apex angle, and the difficulty of control over cutting off the tip part by means of the FIB. Further, the use of the optical fiber makes it difficult to produce a multiple type head which is a means that enhances a data transfer rate.
The method that etches a semiconductor substrate to form a minute opening has such problems as the varying etching rate relative to the opening size of several tens of nanometers, the varying size of the opening due to an uneven thickness of Si substrate relative to a fixed etching amount, and the varying shape of the etched part due to the deviation in the crystal orientation when the semiconductor substrate is cut out. Also, the reverse pyramid form, which is defined by the crystal orientation unique to the semiconductor substrate, may be unable to be regulated to a desired optimum angle. In addition, there is a problem that many steps of stripping and melting the substrate accelerate consumption of materials, leading to a higher cost.
The track pitch in the high density recording, which is hereafter set to 0.1 micrometers or less, makes it difficult to perform positioning of a light irradiation head and a magnetic sensor head with such an accuracy.
In the prior art intended for enhancing efficiency utilizing an optical fiber, however, the conically shaped tip surrounded by a metal results in a position at which incident light causes an electric field concentration to take place due to the lens effect of the conical surface in the optical fiber.
In the above described Non-Patent Document 2, an open face is arranged at the surface on which the electric fields concentrate, for reducing the beam spot and achieving a high efficiency. Although this method is effective, it requires extremely high machining precision, thereby having a problem associated with processing as in the above described case.
In view of the above problems, in the light irradiation head disclosed in the above described Patent Document 3, the tip of the head is formed to be a two dimensional pattern and a high refraction index material is used as the light propagation material in the head, so as to reduce the light or electric field intensity. However, a simple linear form is used as a form of the joint portion between the head and the waveguide that propagates light from a light source to the head, and consideration for a better form is not made.